The GX25 I sold to Willdo in New Zealand was turning my 18-6 Mejzlik about 7500 rpm, about 5 to 700 less than a stock G23.....
The engine was untouched except for trimming the excess from the case and removing the flywheel for CD ignition....Can't remember the weight, it's on a thread here somewhere...
Your thrust test shows how really inaccurate the ThrustHp chart is....